Information is stored on a magnetic recording medium such as a disk as alternating magnetization patterns. As is well known, when a thin film head passes over the recording medium, the magnetization patterns on the medium are sensed to read the information stored on the medium. Alternatively, information is written onto the recording medium by passing a thin film head over the medium to store appropriate magnetization patterns.
A typical disk drive system includes a plurality of magnetic disks and a head assembly. The typical head assembly used with a disk drive moves radially towards or away from the axis of rotation of the disks. At any given discrete distance away from the axis of rotation, the recording head is positioned to read or write data from or to a discrete area on one of the almost concentric tracks of the disk.
To record information onto the magnetic medium, the recording head applies a magnetic field to the portion of the medium within the boundary of the desired track. Ideally, the width of the track should equal the width of the recording head so that the induced magnetic field of the head only alters magnetization patterns of the desired track. The trend in the data storage field is to increase the density of the information stored on a disk. One way to accomplish increased density is to increase the number of tracks on the disk. Accordingly, in a high density disk, the distance between adjacent tracks is smaller than in a low density disk.
If the induced magnetic field of the thin film head extends beyond the width of the head and affects the magnetization position on an adjacent track, the information stored on the adjacent track may be corrupted or destroyed. This problem is referred to as erase fringing. The distance away from the sides of the recording head in the track width direction where the magnetic field erases data on the sides of the recording head is called the erase width of the recording head. The problem caused by erase fringing increases as the ratio of the track spacing to the optical width of the heads decreases in high density disks. Therefore, erase fringing limits the potential density of the magnetic medium or disk because sufficient space between the tracks must be maintained to avoid corrupting or erasing adjacent tracks.
Conventional thin film heads contain two rectangular magnetic poles, P1 and P2, which are separated by a thin gap. Pole P1 is typically made a few microns wider than pole P2 in order to avoid magnetic contact between the two poles due to misalignment in the pole P2 process. The erase fringing that occurs when a magnetic field is applied between poles P1 and P2 increases as the difference in the width of the two magnetic poles at the gap increases. This erase fringing occurs because the magnetic field extends beyond the width of the pole P2 at the gap.
One known method to reduce the amount of erase fringing involves modifying the design of the read/write head. In one such modified design, the air bearing surface (ABS) geometry of pole P1 is modified. The ABS geometry denotes the geometry as seen by the magnetic recording medium looking toward the thin film recording head. The rectangular poles P1 and P2 are milled together so that the width of the resulting rectangular pole P1 is equal to the width of rectangular pole P2 at the ABS. The excess material of rectangular pole P1 and P2 that is milled away extends further away from the ABS past the zero throat point. In this known structure, the length from the ABS to where the milling ceases is approximately 4-6 microns. Accordingly, a relatively large amount of material from pole P1 and P2 must be milled away.
In another modified design for a thin film recording head reducing erase fringing, the ABS geometry of pole P1 is milled to form a relatively rectangular portion adjacent the gap and a relatively trapezoidal portion with a larger cross-section area adjacent the rectangular portion. Again, in this design, the length from the ABS to where the milling ceases is approximately 4-6 microns.
Both of the above modified geometries for a thin film recording head reduce the extent of the magnetic field outside the width at the gap and accordingly reduce erase fringing. However, both of the above head geometries require both poles P1 and P2 to have substantially parallel walls adjacent the gap and to be milled away from the ABS well beyond the zero throat point. Both of these head geometries are difficult and time consuming to manufacture and result in a relatively low yield of satisfactory products during high volume manufacturing.
In one known process for making conventional thin film recording heads with plated poles, a base layer of insulating material such as Al.sub.2 O.sub.3 is deposited on a substrate such as ALSIMAG. A seed layer of material such as NiFe is sputtered over the base layer. Photoresist is next coated over the NiFe seed layer. Next, through a photolithographic process, a window for a pole is formed in the photoresist. After the photoresist is developed, pole material is deposited in the window by electroplating. Now a thin gap layer of material such as Al.sub.2 O.sub.3 is deposited. Then, a coil structure surrounded by insulation is formed at the yoke region of the poles. Finally, the second pole is plated following the same procedure as described above. Normally, the width of the second pole at its tip is plated to be narrower than the width of the first pole at its tip in order to avoid magnetic contact between the poles at the gap. At this point, a conventional thin film head structure has been formed.
If a more specific head geometry is desired, additional track trimming must be done. Using one known technique for trimming the head to the desired geometry, a thick photoresist mask is placed on the desired portion of the second pole and completely over the yoke. Ion milling is now used to remove excess magnetic material not covered by the photoresist along the width of the two pole portions. Therefore, the width of this photoresist pattern determines the final width of the poles at the gap. The ion milling proceeds along the entire excess depth of the first pole portion to achieve two rectangular pole portions of equal width.